A vast body of knowledge exists regarding jaundice in human infants. However, despite this information neonatal jaundice continues to be the most common health problem in human neonates. Many factors have been identified which affect bilirubin metabolism and are associated with either an increase or decrease in the serum bilirubin level. The long term objective of this research is to consolidate and extend current knowledge and understanding of neonatal bilirubin metabolism. The long term outcome of this research would be the development of a practical and clinically useful system which will allow early prediction of which infants are at high risk to develop serious neonatal jaundice. The specific aim of this research is to conduct a prospective study of newborn infants in which a large body of data, all known to be related to bilirubin metabolism, would be gathered. These data would be collected within the first 48 hours of life. Analysis of the data would: (1) identify which variables are of key practical significance in relating to neonatal jaundice levels, and (2) result in the creation of several equations which combine and weight the effects of key variables to predict a jaundice level. These equations would enable differentiation of which infants are at high risk to develop severe neonatal jaundice from those at low risk. Once these predictive equations have been developed, they will be prospectively tested for validity with a subsequent group of patients. This system would be particularly helpful in the management of newborn care because of the early hospital discharge of newborns (less than 24-48 hours of age) widely practiced currently. The quantitation of the risk of severe jaundice would be useful in deciding which infants should be seen for early follow-up as well as which infants should be considered for the various prophylactic and therapeutic measures available today for neonatal hyperbilirubinemia.